Variable autotransformer control



Sept. 3, 1957 J. G. BURSKI VARIABLE AUTOTRANSFORMEIR CONTROL 3 Sheets-Sheet 1 Filed Feb. 24, 1955 INVENTOR. Zea/70rd J 6. Banal z P 1957 1.. J. G. BURSKI 2,805,367

VARIABLE AUTOTRANSFORMER CONTROL Filed Feb. 24, 1955 3 Sheets-Sheet 2 Illl IN VEN TOR. Zea/70rd '1 6'. Ba/1516 ATTOENE Yd Sept. 3, 1957 J. G. BURSKI VARIABLE AUTOTRANSFORMEIR CONTROL 3 Sheets-Shea. 5

Filed Feb. 24, 1955 I II INVENTOR. Leonard J 6. 3401511 ATTOPNEYT tlnited States Patent VARIABLE AUTOTRANSFORMER CONTROL Leonard J. G. Burski, Bristol, Conn, assignor to The Superior Electric Co., Bristol, C0nn., a corporation of Connecticut Application February 24, 1955, Serial No. 490,246

2 Claims. (Cl. 317-) This invention relates to electrical controls, and more particularly to voltage controlling equipment embodying variable autotransformers.

An object of the invention is to provide, in conjunction with a variable autotransformer type of control unit, a novel and improved means for preventing the unit from causing fire in the event that is should become dangerously overloaded or short circuited.

Another object of the invention is to provide a novel and improved voltage control unit embodying a variable autotransformer, which is so arranged and organized as to be readily adaptable for incorporation in the regular Wiring of a building structure and for mounting in the walls thereof, to conveniently control the illumination of any desired, lighted area.

A further object of the invention is to provide an improved, wall-mounted type of voltage control in accordance with the above, which is safe and reliable in use, being so constituted that it will not cause fire in the event of short circuit or overload.

Yet another object of the invention is to provide an improved combination wall-type autotransformer control or dimmer and shut-off switch which is simple, smooth acting, and effective.

A still further object of the invention is to provide an improved assembly of autotransformer control unit and wallbox therefor, which greatly facilitates the installation of the unit, provides for its safe and convenient wiring, enables misalignment of the wallbox to be readily compensated for, and minimizes the likelihood of damage to the autotransformer unit.

Still another object of the invention is to provide a novel and improved wall-box control or dimmer as above characterized, wherein access may be easily and quickly had after installation to the interior of the box, and wherein the control unit per se may be readily dismounted and shifted away from the box to permit its inspection, servicing or replacement.

A feature of the invention resides in the provision of an improved, wall-mounted, autotransformer type of control having overload fuse means arranged for its quick and easy replacement, and for enabling the fuse or the control to be readily tested at any time.

Another feature of the invention resides in the provision of an improved driving connection between the operating knob and shaft, enabling easy and quick yet positive assembly and disassembly of said parts.

A still further object of the invention is to provide an improved voltage control device as above set forth, which is durable and strong, simple in its construction, relatively inexpensive to manufacture, and not likely to easily get out of order.

Other features and advantages will hereinafter appear.

in the accompanying drawings:

Figure l is a front elevational view of a variable autotransformer type of voltage control unit which includes an electrical conduit or outlet box and is arranged for mounting in the wall of a building structure, a portion of Patented Sept. 3, 1957 the face plate of the unit being broken away to reveal details of the underlying structure. The voltage control unit of Fig. 1 is at times referred to as a wallbox dimmer.

Fig. 2 is a vertical sectional view of the voltage control unit of Fig. 1.

Fig. 3 is a rear elevational view of the autotransformer component of the wallbox dimmer, secured to its mounting plate.

Fig. 4 is a perspective view of the outlet or conduit box of the unit.

Fig. 5 is a bottom view of the autotransformer shown in Fig. 3.

Fig. 6 is a fragmentary bottom view of the autotransformer showing a modfication of the invention wherein a fire-preventing means is embodied in the unit.

Fig. 7 is a perspective view of the end portion of the operating shaft of the autotransformer.

Fig. 8 is a schematic circuit diagram of the wallbox dimmer of Figs. 1, 2 and 6.

Fig. 9 is an edge elevational view of a variable autotransformer embodying the novel fire-prevention means of the invention.

Fig. 10 is a right side elevational view of the unit of Fig. 9.

Fig. 11 is a detail showing a fusible link in elevation.

Fig. 12 is a section taken on line 12-12 of Fig. 11.

Referring to Figs. 1 and 2, the improved voltage control unit or wallbox dimmer of the present invention comprises a toroidal type of variable autotransformer indicated generally by the numeral 10, in conjunction with a novel automatic switch mechanism and protective fuse device indicated respectively by the numerals 11 and 12, said components being rigidly secured to a base or mounting plate 13. The assemblage of autotransformer 10, switch mechanism 11, fuse device 12, and mounting plate 13 is housed in an outlet or conduit box which is of generally rectangular shape, said box being closed by a face plate 15 secured, by means of screws 16, to the mounting plate 13.

The face plate 15 has openings to receive an operating shaft 16 of the autotransformer unit 10 and also a tubular housing 17 of the fuse device 12, said shaft and housing projecting through and forwardly from the plate 15. The operating shaft 16 of the autotransformer unit carries a large-diameter, flat, circular operating knob 18, said knob having an index mark 18a and also peripheral knurling 19 by which it and the shaft may be conveniently turned to operate the transformer 10.

In accordance with the present invention the shaft 16 and knob 18 are so arranged as to provide a novel, interfitting driving connection which enables easy and quick yet positive assembly and disassembly of these parts. Referring to Figs. 1 and 7 the end portion of the shaft 16 is provided with a diametric, axially-extending slot 16a and further provided with a flat 16b disposed at right angles to and intersecting the slot 16a. The knob 18, Fig. 1, has a rib 18b adapted to be received in the slot 16a of the shaft, and has a flat bore portion engageable with the flat 16b of the shaft. The knob 18 may thus be carried by the shaft 16 in only one position, insuring that the index mark 18a will always be properly located with respect to the off and on" settings. By virtue of the provision of the slot 16:: in the end portion of the shaft, the latter is slightly resilient in that the two extremities of said end portion are yieldable to an extent with respect to cath other. By virtue of this, a close fit may be established between the shaft 16 and the bore of the knob 18 while still permitting ready assembly and disassembly of the knob from the shaft without any tendency toward looseness.

The autotransformer 10 has a toroidal winding 20 provided with a commutator surface 21 engageable by a carbon brush (not shown) carried by a brush assembly 22, Fig. 3, which is in turn rotatably carried by a heat-radiating wheel 23 secured to the shaft 16. The radiator wheel 23 may be advantageously formed of aluminum and so arranged as to carry heat from the brush assembly 22 and dissipate the same as is already well known in the art.

Referring to Fig. 8 the toroidal coil is shown diagrammatically, being engaged by a slider in the form of a carbon brush which for the sake of convenience of illustration is designated by the numeral 22 given to the brush holder in Fig. 3. Considering Figs. 1 and 8 when the index 18a of the knob 18 is at the off position the brush 22 in Fig. 8 will be adjacent the lower extremity of the winding 20, close to an output lead 23 from said extremity. When the knob 18 is rotated clockwise, as viewed in Fig. l, to bring the index mark 18a adjacent the on" position, the brush 22 in Fig. 8 will be at the upper extremity of the coil 20, virtually connected to an input lead 24 joined to said extremity. A second input lead 25 is provided, for connection to the output lead 23 and to the lower extremity or end of the coil 20, as will be understood, and by this circuit the coil 20 will be energized across its ends from the input and will deliver a variable voltage between the output lead 23 and a second output lead 26 connected with the brush 22.

In accordance with the present invention I provide a novel and improved, smooth-acting automatic switch mechanism in conjunction with the variable autotransformer 10 by which the coil 20 thereof is automatically deenergized when the knob 18 is positioned with its index mark 18a at the off position shown in Fig. 1.

Referring to Fig. 3. this improved switch mechanism comprises an on-off snap switch 27 which may be of the type known in the art by the trade-mark Microswitch. The switch 27 is secured to a horizontal shelf 28, Figs. 2 and 3, which is preferably formed of insulating material, said shelf being mounted between rearwardly-extending arms or brackets 29 formed integral with the mounting plate 13. The switch 27 has a resilient actuating arm 30 provided with a rounded extremity 31 for engagement with the periphery of the radiator wheel 23, and the latter has a wide notch 32 in its periphery, providing clearance for the actuating arm 31 of the switch when the autotransformer is in the olf position indicated in Fig. l.

The peripheral portion of the radiator wheel 23 is provided with an annular groove, and a circular piece of spring wire 33 having inwardly bent ends 34 is snapped into and retained by said groove, to act as a bearing for the switch actuator arm 30. When the radiator 23 is in the position shown in Fig. 3 the switch 27 will be open, and for other positions of the radiator wheel, corresponding to various adjusted positions of the knob 18, the switch 27 will be closed, as effected by engagement of the switch actuator arm 30 with the bearing wire 33.

I have found that with the above organization a very smooth and reliable automatic actuation of the switch 27 is effected, using parts that are relatively simple and inexpensive to produce. The action is such that the switch 27 may be actually heard to go on and off, and in addition a tactile indication is had since the user can readily feel. through the knob 18, the actuation of the switch arm 30.

For the purpose of enabling certain circuit tests to be easily made during and after installation, and for preventing damage to the autotransformer unit 10 due to overloading, short circuits in the output circuit, etc., I provide the readily accessible fuse device 12 comprising the tubular housing 17 which is rigidly secured to the mounting plate 13. Referring to Fig. 8, the fuse 12 may be inserted in the output lead 26 and may be advantageously on the order of three amperes capacity when the autotransformer is rated at 360 watts.

Removably carried by the housing 17 of the fuse is an insulated cap 36 which retains in place a cartridge fuse element 37, Fig. 2, in the usual manner. By virtue of the fuse cap 36 being accessible at the front of the face plate 15, the checking and replacement of fuses may be quickly and conveniently accomplished without requiring disassembly of the control unit.

Moreover, in accordance with this invention, by mounting both the switch mechanism 11 and the fuse device 12 so that they are carried by the mounting plates 13 along the autotransformer unit 10, all of these components may be completely wired to each other and will constitute in effect a unitary device, greatly simplifying the installation and servicing procedure.

As shown in Figs. 2 and 3, the various lead wires 38 may be formed into a harness 39 and secured by a clamp 40 to one of the rearwardly-extending arms 29 of the mounting plate 13. By this organization there is prevented any likelihood of the lead wires being pulled loose from their connections during installation or servicing of the unit.

By the present invention means are provided by which the autotransformer 10 is prevented from causing a fire in the event of a short circuit or sustained overload or other abnormal condition. As shown in Figs. 3, 5 and 8 I provide a heat-responsive cutout unit 41, mounted on the horizontal shelf 28 in close proximity to the autotransformer 10. The cutout 41 may be of a construction employing a snap disk which responds to heat by opening the circuit, and responds to cooling by automatically again closing the circuit. The thermal cutout 41 is indicated in Fig. 8 as being inserted in the input lead 24 whereby it will disconnect said lead from the coil 20 in response to dangerous, elevated temperatures and thereby prevent heating which might cause combustion.

According to the invention I may employ either in conjunction with the thermal cutout 41 or as an alternative thereto a fusible, electrically-conducting link 42, Fig. 6. The fusible link 42 may be made of soft metal having a low melting point, such as a lead-tin alloy and may be disposed in intimate heat-exchanging relation to the coil 20 as shown. In Fig. 8 the fusible link 42 is also shown as connected in the input lead 24 of the device, and when a dangerously high temperature is reached the link 42 will melt and permanently open the circuit until it is again reclosed by a service operation. Preferably the fusible link 42 is enclosed in an insulating sheath of plastic or woven fibers or the like.

It will be noted from Fig. 6 that the link 42 has a direct connection with the end of the coil 20 and accordingly it not only receives heat directly therefrom by conduction but also receives heat through radiation. Accordingly the link 42 will be sensitive in its response to overheating of the coil. With either of the thermal cutouts 41 or 42 there is prevented any likelihood of the autotransformer unit 10 causing a fire due to its being overloaded or becoming short circuited or the like.

The assemblage of mounting plate 15, autotransformer 10, switch mechanism 11 and fuse device 12 is thus seen to be so organized and arranged as to readily adapt it for mounting in the wall of a building structure and for connection to a conventional wiring system. For these purposes and others to be described later I provide, in conjunction with said assemblage, an improved outlet or conduit box which enables the assemblage to be readily mounted in it and also aligned with the vertical. yet the assemblage may be easily dismounted and shifted out of the box for installation and servicing purposes.

This outlet box is shown in perspective in Fig. 4 and indicated generally by the character 45. The box 45 is substantially rectangular in shape, having a back wall 46, left and right side walls 47 and 48, top wall 49 and a bottom wall 50. For the purpose of positioning the mounting plate 13 at the front of the box 45, pairs of shoulders 51 and 52 are provided, engageable with corner portions of the mounting plate 13. The pair of shoulders 52 is disposed intermediate the top and bottom walls 49 and 50 of the box, as shown.

The shoulders 51 and 52 are formed by fabricating the box 45 with inwardly offset portions or columns 53 and 54, the columns 53 being located in the upper corners of the box, as may be observed. The columns 53 and 54 have no end or rear walls but instead provide an indented configuration to the rear wall 46 of the box 45, and by this construction the box 45 may be readily fabricated as a casting without resorting to complicated dies having movable inserts. It will be understood that if the shoulders 51 and 52 were to be provided in a cast box without the columns 53 and 54 it would involve a difficult casting procedure and a complicated die. However, by the provisions of the columns 53 and 54, the box 45 may be readily pulled from a relatively simple cavity without the necessity of employing movable or retractible wall parts.

To provide for easy and quick aligning of the control assemblage with the vertical even though the box 45 may not be mounted squarely in the wall, I provide arcuate slots 55 in the corner portions of the mounting plates 13, to receive screws 56, Fig. 1, which are threaded into tapped holes 57 in the shoulders 51 and 52. In conjunction with the slots 55 I make the mounting plate 13 smaller in height and width than the box 45, thereby to enable the mounting plate to be arcuately shifted either clockwise or counterclockwise when it is carried by the box 45. By this organization it is possible to readily compensate for crooked positioning of the outlet box as it is supported by the wall structure of the building.

For the purpose of protecting the control unit against inadvertent damage during installation, the box 45 is provided with a transverse partition 58, Figs. 1, 2 and 4, providing a large upper cavity in the box to accommodate the control unit and a smaller lower cavity to accommodate the wiring. The partition 58 has a notch 59 through which the wiring harness 39 may extend, so that the lead wires 38 from the unit may be readily brought into the lower or wiring compartment.

It will be appreciated from an inspection of Figs. 1 and 2 that when the control assemblage is mounted in the upper compartment 61 of the box 45 the partition 53 will protect it against damage during the use of tools such as are ordinarily employed in connecting wiring. The walls of the lower or wiring compartment of the box 45 are formed to have the usual knockouts 69 to provide for the entrance and exit of electrical conduit and cable, as is well understood.

With the above organization, the installation of the control unit is greatly facilitated. If at any time it becomes necessary to have access to the autotransformcr, switch or fuse mechanisms, etc., the user is merely required to remove the knob l3 and face plate 15, and then loosen and remove the screws 56 which fasten the mounting plate 13 to the outlet box 45. The assemblage carried by the mounting plate may then be pulled out of the box without diconnecting any of the leads, and quick, complete access to the unit is thus possible without any difiiculty.

The partition 58 in effect converts the box 45 into two, joined enclosures or boxes having said partition as a common wall, and the upper of said enclosures, namely the upper compartment 61 may then be thought of as having the supporting shoulders 51 and 52 adjacent its corners. Thus it will be seen that the base or mounting plate 13 is adjustably supported in the compartment 6i. by cooperable means on said plate and on the box, said means being disposed adjacent the corners of the plate and the box, considering the latter as being constituted of the upper compartment 61.

From the foregoing it will be understood that I have provided an improved, variable autotransformer type of control and associated protective devices so arranged and organized as to be readily adaptable for mounting in the wall of a building structure and for incorporation in the wiring system thereof. The organization is characterized by relatively few parts of simple yet sturdy construction, which may be economically fabricated. The control is effective and foolproof in operation, and provides an ellicient means for varying the illumination of any desired lighted area in a building.

A modified form of autotransformer type of control embodying the fire prevention features of the invention is shown in Figs. 9 through 12. In these figures there is shown an autotransformer comprising a frame 62 supporting a toroidal core 63 and coil 64 wound thereon. The autotransformer has a shaft 65 carrying a radiator wheel 66 on which a brush assemblage 67 is mounted, including a brush 68 bearing against a commutator surface 69 of the coil 64.

The frame 62 has a terminal board 70 mounting a center terminal 71 connected with the brush 68, and end terminals 72 and 73, the latter being connected with one end 73a of the coil 64. By the present invention the other end 74 of the coil 64 is connected to a post 74a and said post is connected by a fusible link 75 to the terminal 72. The link 75 is constituted of a soft wire 76 of low melting point metal. The fusible wire 76 may be of lead-tin alloy, and as shown in Fig. 11 it may have a core 77 of soldering flux such as rosin or the like. I have found that by the use of a flux core in the fusible wire there is less tendency for splattering to occur when the wire melts. Preferably the link 75 is covered with an insulating sheath 78 which may be of extruded plastic material, woven fibers or the like.

When an autotransformer type of control such as that shown herein is provided with the fusible element or link 75 the latter may be so arranged that, for serious abnormal circuit conditions, it melts and opens the circuit before the unit can get hot enough to cause a fire. Even though portions of the coil 64 of the autotransformer which are remote from the fusible link 75 should experience the greatest heat, this heat will disperse throughout the toroidal core 63 and coil 64 and react on the link 75 to cause timely melting of the latter.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

I claim.

1. A voltage control unit adapted to be incorporated in a wall of a building for controlling the brilliance of lights comprising a variable autotransformer having input leads and output leads and a projecting operating shaft; a base plate on which the autotransformer is mounted and having an opening through which said shaft extends; an electrical conduit box in which the autotransformer is disposed and having an open front; said box and base plate having cooperable means for detachably connecting the plate to the box with the autotransformer disposed within the box; a heat-responsive switch connected to the input leads of the autotransforrner and mounted on the base plate and disposed within the box and responsive to the temperature within the box for opening the circuit to the autotransformer upon abnormal temperatures being attained within the box; means on the base plate, pro viding a socket open at the front of the plate; a removable cap for the said socket forming means; a fuse mounted in said cap and socket means and connected in the output leads to open the circuit in the event of an overload; a partition in the box providing a compartment separate from the interior of the box and having an opening through which the input and output leads extend, said partition constituting a guard to prevent the entrance of tools and wiring fittings into the interior of the box;

and a face plate extending across the open face of the interior of the box and the compartment and detachably secured thereto, said plate having an opening in registration with the opening of the base plate through which the shaft of the autotransforrner extends; a knob disposed exteriorly of the face plate and mounted on the shaft for permitting actuation of the latter to operate the autotransformer; and said plate having a further opening through which the cap extends to facilitate access and replacement of the fuse.

2. The invention as defined in claim 1 in which the autotransformer includes a radiator wheel mounted on the shaft, and having a notch in its periphery, a switch mounted on the base plate and having a switch arm slidably engaging the periphery of the Wheel, and connections connecting the switch in the input leads, whereby the switch opens the input circuit when it engages the notch.

References Cited in the file of this patent UNITED STATES PATENTS 

